The primary mission of the Gastric Histopathology Core is to provide high quality, rapid-turnaround histology and immunohistochemistry services to investigators in this PPG, and to provide expert histopathologic nterpretation, through collaboration with Dr. Kay Washington. The following services are proposed: 1. To provide high quality, rapid-turnaround research histology services to PPG investigators. 2. To provide expert evaluation of histopathology of rodent models of H. pylori-Induced gastric neoplasia and correlation with human disease. 3. To provide expertise in developing, performing and evaluating immunohistochemical studies on animal tissues. 4. To provide laser microdissection services. 5. To perform quality control to ensure that histology and immunohistochemistry services are of highest quality. 6. To provide tissue microarray services and access to human gastric tissue samples as needed. The three component projects and Core B (Proteomics Core) of this proposed Program Project all rely heavily upon morphologic analysis of gastric tissues isolated from rodent models of Helicobacter pyloriinduced gastritis and gastric neoplasia. Dr. Washington's expertise in interpretation of histopathologic changes in rodent models and in interpretation of immunohistochemical studies will be critical to this work, and this collaborative activity is currently not funded through existing resources. By utilizing the resources of an established Research Histology facility for tissue storage, processing, cutting of blocks, and staining of slides, it will be possible to achieve high standards for all histologic studies proposed in this grant. This centralization of histologic services under the supervision of a surgical pathologist with a dedicated interest in gastrointestinal pathology will allow careful attention to quality assurance.